All Electrical is Dead, but Batteries check Good

[R Schwartz]

2004 (early '04) Chevrolet Silverado K3500 6.6L Duramax diesel dually.  Truck started blowing black smoke but seemed to be running fine, no skipping, bucking or hesitation.  I only drove it about 80 miles to get back home and parked the truck.  When I went back to troubleshooting after 5 days the truck is completely dead.  Electronic key entry, all cabin lights, all dash lights, brakes go to the floor, everything!!  Batteries read over 12V.  Checked all grounds, clean and tight.  I would like to troubleshoot as much as I can to avoid paying for hours and hours of tech time at a shop.

[CamGTP]

Checking fuses is the best start. Something is not working if the battery has voltage but things inside the truck do not.

[Jsdirt]

Battery or batterIES could be completely smoked. You can have 12V, but if it can't reach the rated amperage, you might as well have 6V. 

 

Check voltage again with the key on, then the headlights or some other high load (glow plugs pull pretty heavy, too) - if it drops way down below 11V fast, the battery (or both) is (are) spanked.

Edited January 6, 2025 by Jsdirt